Generally, as a construction machine, a hydraulic excavator is constituted by a vehicular automotive lower structure, an upper revolving structure which is rotatably mounted on the automotive lower structure, and a working mechanism which is provided liftably on a front portion of the upper revolving structure.
The upper revolving structure is largely constituted by a revolving frame, an engine which is mounted on the rear side of the revolving frame, a counterweight attached to a rear end portion of the revolving frame on the rear side of the engine, a flat plate-like floor panel provided on the revolving frame on the front side of the engine, an operator's seat provided on the floor panel, and a housing or cover structure like a canopy or a cab which is provided overhead the operator's seat.
Among hydraulic excavator type construction machines are small-size hydraulic excavators which are generally called “mini shovels”, and are preferably used at small-spaced working area. In the case of a small-size hydraulic excavator which lacks spaces for accommodating various equipments, it has been the usual practice to locate control valves, revolving motor and associated equipments under a floor panel.
On the other hand, upon lifting a rear end portion, the floor panel is turned about a supporting point at its fore end and tilted up to permit an access to control valves, revolving motor or other equipments which are located under the floor panel, for example, at the time of maintenance and service.
More particularly, a floor support mechanism is provided between front side of the revolving frame and a front end of a floor panel thereby to tiltably support the floor panel, permitting to tilt up the floor panel in forward or rearward direction turning about a supporting point at a fore end of the floor panel together with an operator's seat. In addition, gas dampers are provided between the lower side of the floor panel and the revolving frame, so that the floor panel can be tilted up in the forward direction by biasing force of the gas dampers, turning about a supporting point on the floor support mechanism (e.g., Japanese Patent Laid-Open No. 2000-72048).
In the case of the hydraulic excavator according to the above-mentioned prior art, the floor panel is tilted up by biasing force of gas dampers which are provided on the lower side of the floor panel. However, a great weight is put on the floor panel by the operator's seat, cab, levers, pedals, valves, indicators and instruments, and air conditioner which are installed on the floor panel. Therefore, in the above-mentioned prior art, two to four gas dampers are provided to lift up the heavy floor panel.
However, in case two to four gas dampers are provided under a floor panel, they stand as an obstacle in the way of a service man even when the floor panel is tilted up for the purpose of maintenance and service, obstructing to reach an equipment which needs inspection or repair work and thus making it difficult to perform maintenance jobs in an efficient manner.
Besides, dampers which are accommodated under a floor panel are limited in size, particularly in stroke length, and therefore unable to tilt up the floor panel through a large angle. If gas damper positions are brought closer to a supporting point for tilting the floor panel through a larger angle, it becomes necessary to apply a greater force by the use of gas dampers of an objectionably large size or by the use of an objectionably large number of gas dampers.
On the other hand, the gas dampers are constantly biased force in the direction of uplifting the floor panel, so that, as soon as a lock is canceled to tilt the floor panel, the gas dampers in a contracted state are stretched to a fully expanded state at one stroke. Therefore, the floor panel is abruptly lifted up as soon as a lock is canceled to tilt the floor panel. In addition, there is still another problem that a great force is required for pushing down the floor panel against the biasing force of the gas dampers.
Furthermore, in case of gas leaks due to deterioration of a seal member, it becomes difficult for the gas dampers to hold the floor panel in the tilted state. This problem gives rise to another problem that a stopper has to be provided between the revolving frame and the floor panel thereby to hold the floor panel in a lifted state even in the event of gas leaks from the gas dampers.